Generally, a wireless communication system that includes a base station (BS) and a user equipment (UE) provides the user equipment with various kinds of communication services including voice or data through one or more base stations. Generally, one base station may provide one or more cells.
The recent trend in a structure of the wireless communication system is that a macro cell based centralized base station type corresponding to a conventional vertical layer is being switched to a base station type in which various types of small cells such as a pico cell and a femto cell interact with a macro cell.
Meanwhile, as efforts to reduce the greenhouse effect and environment destruction, which are caused by excessive emission of CO2, have been increased, an element that best emits CO2 in the field of mobile communication is regarded as a power of a base station, and an important issue is how the power of the base station may be reduced or how the power of the base station may be used efficiently.
It has been until recently focused on efficient use in a power of a user equipment and decrease of energy consumption of the user equipment to increase portability of the user equipment. However, in the future, the power of the base station may be used efficiently to reduce energy consumption, whereby emission of CO2 may be reduced and operation expenditure (OPEX) may be saved.
Therefore, the need of technology development for reducing power consumption of the base station through efficient energy consumption of the base station has been increased, and from Release 9 in the 3GPP (3rd Generation Partnership Project), energy saving solution in view of the base station has been discussed, and in Release 12, technologies for energy saving of long term evolution (LTE) base stations at an off-peak time have been discussed.
For energy saving of the base station, it may be considered that the base station is shifted to a power-off state or idle mode. In this case, the base station that is shifted to the power-off mode or idle mode may perform handover for user equipments located in its coverage area to neighboring base stations that may compensate for a coverage of the base station.
However, since there is no separate signaling procedure between the base station and the neighboring base stations, a problem may occur in that the neighboring base stations may not compensate for the coverage of the base station normally, whereby handover may be failed or service quality may remarkably be deteriorated.
In particular, when the base station supports MBMS (multimedia broadcast/multicast service), since the base station does not have a separate signaling procedure with a neighbor base station, the base station and the neighbor base station may be unaware of whether or not the base station and the neighbor base station support the MBMS.
Under this situation, if it is determined to compensate for coverage of the base station by the neighbor base station, the base station performs a transition to a power-off state or an idle state. In this case, the neighbor base station attempts to compensate for the coverage of which the MBMS service used to be provided by the base station. Yet, if the neighbor base station corresponds to a base station not supporting the MBMS, user equipments, which have been received the MBMS service from the base station, are unable to receive an MBMS signal anymore. Hence, service interruption may occur.
Therefore, it is necessary to introduce a method capable of compensating for the coverage of the base station without a missing part and a solution for the same.